In Patent Reference 1, for example, there is disclosed a tide gate apparatus which opens or blocks an opening of a lock gate installed in a seawall or embankment on a seacoast or near a mouth of a river.
In the tide gate apparatus of the lock gate according to Patent Reference 1, a door body is raised to prevent seawater from flowing into an opening of the lock gate, by causing a bypass circuit of a hydraulic device to open, which causes the tide gate to rise due to a water pressure and a buoyancy of the seawater.
However, in the tide gate apparatus of the lock gate according to Patent Reference 1, if the lock gate is damaged by a wheel load of a vehicle traveling above the lock gate when it is in a lowered state, there is a problem that the lock gate cannot float when water flows into an inner part of the lock gate from the damaged portion.
Moreover, if the lock gate is damaged by a water pressure of a tsunami or a high tide when it is in a raised state, there is a problem that it becomes impossible to maintain the raised state when water flows into an inner part of the lock gate from the damaged portion.
Patent Reference 1: Japanese Patent No. 4,388,494